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<br />3366
<br />
<br />For the 2003 detem1ination, Reclmnation recognizes and takes into account the unique
<br />location and irrigation system faciJjties used by lID, Reclamation also concludes that the
<br />geographic locations of all facilities and irrigated areas within liD have not changed in
<br />recent years in any maImer affecting this annual detennination,
<br />
<br />FACTOR 2, CLIMATIC CONDITIONS
<br />
<br />Part 417,3 identifies climatic conditions as a factor to be analyzed, The chmate oflhe
<br />Imperial Valley is stable (JensenlWalter Supplement 2003, p, I), The Imperial Valley is
<br />known generally for high sunm1er temperatures and low rainfall, The annual mean
<br />temperature is about 730 Fahrenheit (0 F), with the highest 1I10nthly mean temperature of
<br />95,90 I' in August. The average annual precipitation recorded in the valley from 1914 to
<br />1998 was 2,93 inches (NRCE, March 2002, p, III-I),
<br />
<br />Reclamation used climatic infonnation for this determination trom three California
<br />Irrigation Management Information System (CIMIS) weather stations located in the
<br />Imperial Valley and within lID (Jensen/Walter Supplement 2003, p, 2, Jensen/Walter
<br />1997; Jensen 1995, and others), These stations have the longest CIMIS record in IlD, are
<br />reliable, and widely used to calculate crop water requirements,
<br />
<br />Climatic data are used to calculate crop evapotranspiration (ET,), the primary component
<br />of irrigation water use, Crop evapotranspiration (ET,) represents the water actually used
<br />by the plants plus the amount of water that naturally evaporates from the soil after an
<br />irrigation or precipitation event,
<br />
<br />Infonnation and data from the Mulberry, Seeley, and Meloland CIMIS stations for
<br />rainfall, solar radiation, humidity, temperature and wind speed were collected and used in
<br />subsequent formulas and computations for both the reference crop evapotranspiration
<br />(ETo) and the similar crop evapotranspiration (ET,) calculations fur each crop WIthin [lD
<br />that are presented later in Factor 12 of this determination, These same three stations and
<br />parameters of climatic data were also relied upon by lID (NRCE 2002, p, 111-3 and
<br />Appendix 4), by MWD (MET: Allen, Memorandum for Annual Crop ET, 2003, p, I),
<br />and by CVWD (WAC: Gilley, et aI., 2003, p, 104) for completing similar, yet separate,
<br />estimates of crop evapotranspiration (ET,),
<br />
<br />Reference crop ET (ETo) is a measure of the evaporative demand of the atmosphere,
<br />stated in inches of water. Reference crop ET (ETo) incorporates all tbe parameters of
<br />climate that are impot1ant to crop production (rainfaJl, solar radiation, humidity,
<br />temperature and wind speed) into a single statistical measure, It is the measure that
<br />irngatlOn scientists conU1lOnly use to express a numeric value for climate, as it relates to
<br />growing plants,
<br />
<br />.July 2, 2003
<br />
<br />15
<br />
<br />Detemlinations and Recommendations
<br />For 110 - Calendar Year 2003
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